Celluloses obtained by milling cellulose-containing raw materials such as pulps have been used as industrial materials such as raw materials of cellulose ethers, cosmetics, food stuffs and biomass materials. Among them, celluloses having a crystal structure thereof decrystallized are especially useful as these industrial materials.
For example, there is known the method of producing powdery pulps by mechanically treating sheet-like pulps using a mill (e.g., refer to Patent Documents 1 and 2). However, in these Patent Documents, there are no descriptions concerning the crystallinity of the celluloses.
Also, there is known the method of mechanically treating pulps using a mill to reduce the crystallinity of celluloses in the pulps (e.g., refer to Patent Documents 3 to 6).
In Examples 1 and 4 of Patent Document 3, there is disclosed the method of treating sheet-like pulps using a vibration ball mill or a twin-screw extruder.
In Examples 1 to 3 of Patent Document 4, there is disclosed the method of treating pulps using a ball mill.
In Examples 1 and 2 of Patent Document 5, there is disclosed the method of treating cellulose powders obtained by subjecting pulps to chemical treatments such as hydrolysis using a ball mill and further an air mill.
Patent Document 6 discloses the method of treating pulps kept dispersed in water using a media-type mill such as a vibration ball mill.
However, these methods have failed to achieve satisfactory efficiency and productivity when reducing the crystallinity of the celluloses.    Patent Document 1: JP 5-168969A    Patent Document 2: JP 2001-354701A    Patent Document 3: JP 62-236801A    Patent Document 4: JP 2003-64184A    Patent Document 5: JP 2004-331918A    Patent Document 6: JP 2005-68140A